I couldn't decide between this fine drawing:
[which is the Medowlark, and happens to be the Nebraska state bird and the mascot of my elementary school, the May Morley Medowlarks]
Or this one:
[which is obvioulsy an awesome scary scavenger eating the head of a deer]
Whatever your style, you will find something to ooh and ah over in the online version of Audubon's Birds of America. Its even fun to just look at the bird names, which are often hilarious. I also like the scetches of interior bird anatomy.